How do you hide UV seams?
Select your rock, in edit mode clear all seams, mark another set of seams different from the previous set, create a new UV map (name it "target"), unwrap the mesh, in the image editor create a new blank image and save it to the HD. 

Go to the render tab, Bake tab: Bake Textures.
This procedure creates a 2D image - with visible seams - that can be doctored with a 2D image editor and then used as texture with the "target" UV map.
Make sure not to touch the borders of your new image while doctoring, or you'll create new visible seams.